Bronchodilator agents play an outstanding role in the treatment of respiratory disorders such as COPD and asthma. Beta-adrenergic agonists and cholinergic muscarinic antagonists are well established bronchodilator agents in widespread clinical use. Beta-adrenergic agonists currently used by the inhaled route include short-acting agents such as salbutamol (qid) or terbutaline (tid) and long-acting agents such as salmeterol and formoterol (bid). These agents produce bronchodilation through stimulation of adrenergic receptors on airway smooth muscle, reversing the bronchoconstrictor responses to a variety of mediators, such as acetylchollne. Inhaled muscarinic antagonists currently used include the short-acting ipratropium bromide or oxitropium bromide (qid) and the long-acting tiotroplum (qd). These agents produce bronchodilation by reducing vagal cholinergic tone of airway smooth muscle. In addition to improve lung function, these agents also improve quality of life and reduce exacerbations. There are in the clinical literature a number of studies strongly demonstrating that the administration of a combination of a beta-2 agonist and a M3 antagonist is more efficacious for the treatment of COPD than either of the components alone (for example, van Noord, J. A., et al., Eur. Respir. J., 2005; 26: 214-222). Pharmaceutical compositions containing a combination of both types of bronchodilator agents are also known in the art for use in respiratory therapy. As an example, WO2009013244 discloses a medical composition containing salmeterol as beta-adrenergic agonist agent and tiotroplum as antimuscarinic agent.
The class of beta2 adrenergic is well known and widely used by the persons skilled in the art, such as physicians, pharmacists or pharmacologists, for the treatment of respiratory disease, in particular asthma and chronic obstructive pulmonary disease (COPD) (Paul A. Glossop et al., Annual Reports in Medicinal Chemistry, 2007, 41, 237-248). Most of the beta2 adrenergic agonists are derivatives of natural catecholamines (e.g. epinephrine and norepinephrine) with which they share some common structural features, which are responsible for the similar interaction of these compounds with the beta 2 receptors (“Goodman & Gilman's The Pharmacological Basis of Therapeutics”, 10th edition, chapter 10, pages 215-233, Textbook of respiratory medicine, third edition, Chapter 11, p. 267-272). In fact, most of the beta2 adrenergic agonist compounds have a general structure type that is present in the catechol (epinephrine and isoproterenol), namely an aminoethanol core flanked by an aryl group (J. R. Jacobsen, Future Medicinal Chemistry, 2011, 3 (13), 1607-1622). Examples of the aryl group that afford beta2 potency are but not limited to catechol, saligenin, formamide and 8-carbostyril groups (Paul A. Glossop et al., Annual Reports in Medicinal Chemistry, 2007, 41, 237-248).
Dual-pharmacology muscarinic antagonists-beta2 agonist (MABA) molecules present an exciting new approach to the treatment of respiratory disease by combining muscarinic antagonism and beta2 agonisn in a single entity. In the literature there have been disclosed various compounds having both muscarinic receptor antagonist and beta2-agonist activity (A. D. Hughes et al., Future Medicinal Chemistry, 2011, 3(13), 1585-1605). All of these molecules possess a great variety of covalent linker fragments between the M3 antagonist and the beta2 agonist moieties, indicating that the structure of the linker radical is not critical to preserve both activities, although such linker fragments has showed to be an important tool for modulating physical properties and potency at each target.
A single molecule possessing dual activity at muscarinic M3 and adrenergic 32 receptors (MABA) would therefore be desirable both in terms of efficacy and side-effects in the treatment of COPD. It would show also a relevant advantage in terms of formulation compared with the two-component combination. It also would be easier to co-formulate with other therapeutic agents such as inhaled anti-inflammatories to create triple therapy combinations. Thus there is a need for new compounds having both beta2 receptor agonist and muscarinic receptor antagonist activity and being suitable for the treatment of respiratory diseases, such as asthma and COPD.